1. Field of the Invention
The present invention relates to a display apparatus that will not fail to display a closed-caption superimposed on a component video signal provided thereto.
2. Description of the Background Art
In FIG. 5, the structure of a conventional display apparatus, typically a television receiver, is schematically shown. A conventional display apparatus PA includes a color-difference signal demodulator 1, a sync-separator 2, a closed-caption (hereinafter abbreviated as CC) decoder 3, an RGB processor 4, and a display 5.
The color-difference signal demodulator 1 demodulates a luminance signal Y and a chroma signal C of NTSC into a color-difference signal U (B-Y) and a color difference signal V (R-Y). The sync-separator 2 separates and extracts a horizontal synchronization signal H-SYNC and a vertical synchronization signal V-SYNC from the luminance signal Y.
The CC (Closed-Caption) decoder 3 extracts data from a closed-caption signal, which is a VBI signal superimposed on the NTSC video signal at the 21H of the first field. Further, the CC decoder 3 decodes the extracted data into RGB display signals and a switching signal Ys for on-screen display process. The RGB processor 4 demodulates component video signals Y, U, and V into RGB signals. The display 5 is structured by a CRT and other components, and displays an image based on the RGB signals.
The operation of the above display apparatus PA is now briefly described. A conventional NTSC composite video signal is separated into the luminance signal Y and the chroma signal C. These separated signals Y and C are then demodulated by the color-difference signal demodulator 1 into a component video signal Scv (not shown) composed of the luminance signal Y, the color-difference signal U, and the color-difference signal V. Note that the luminance signal Y and the chroma signal C may be provided via a so-called S terminal.
The luminance signal Y is provided to the color-difference signal demodulator 1 and also to the sync-separator 2. The sync-separator 2 separates the horizontal synchronization signal H-SYNC and the vertical synchronization signal V-SYNC from the luminance signal Y, and then outputs the separated signals to deflection circuits in the CC decoder 3 and the display 5.
The CC decoder 3 extracts the caption data from the closed-caption signal superimposed on the luminance signal Y. The CC decoder 3 also generates the RGB signals R, G, and B and the switching signal Ys that are synchronized with the synchronization signals H-SYNC and V-SYNC provided by the sync-separator 2, and outputs the generated signals to the RGB processor 4.
The RGB processor 4 switches, or exclusively selects the source of the RGB signals to be received based on the switching signal Ys. That is, if the switching signal Ys is invalid, the RGB processor 4 converts the luminance signal Y and the color-difference signals U and V provided by the color-difference signal demodulator 1 into RGB signals (R, G, B) for output. On the other hand, if the switching signal Ys is valid, the RGB processor directly outputs the RGB signals (R, G, B) provided by the CC decoder 3 to the display 5.
In FIG. 6, an example of the waveform of the closed-caption signal superimposed on the NTSC video signal (luminance signal Y) is shown. As stated above, a closed-caption signal Scc is multiplexed (superimposed) on the 21H of the first field of the NTSC video signal. The closed-caption signal Scc is synchronized with a clock during a clock line CL.
The closed-caption signal Scc is composed of a start bit SB (represented by S in FIG. 6) and a 16-bit (2-byte) data stream DS that include 2-byte-type control data, one-byte-type character data, and 2-byte-type special character data. A color burst signal is inserted between the clock line CL and the horizontal synchronization signal H-SYNC. A detailed description of the closed-caption code system is provided in FCC 91-119 and FCC92-157 by Federal Communications Commission (FCC). Therefore, further description is omitted herein.
In the conventional display apparatus as described above, closed-caption data can be extracted if the closed-caption data signal Scc is superimposed on the NTSC video signal, but cannot be extracted if superimposed on the component video signal. In other words, the conventional display apparatus does not support such a case where a closed-caption signal is superimposed on the luminance signal Y from upcoming video equipment having a terminal for a component video output composed of the luminance signal Y, a color-difference signal PB (Cb), and a color-difference signal PR (Cr).
Various video signal modes such as 480i, 480p, and 1081i are expected for digital broadcasting. Presently, video signals of such modes are received and demodulated by an STB (Set-Top Box), outputted as components Y, PB, and PR, and coupled to a display apparatus such as a television receiver. Of these video signal modes, a signal of the 480i-interlace mode is more likely to have a closed-caption signal superimposed thereon. In such a case, when signals of the other modes are decoded, a closed-caption will be erroneously detected.
In other words, it is assumed in the display apparatus PA, as in a non-progressive DVD player, that only the 480i-interlace video signal is outputted. However, when progressive DVD players emerge, instead of the 480i-interlace video signal, a 480p-progressive video signal of 480 valid scanning lines may be provided. Furthermore, when digital television broadcasting starts, a 1080i-interlace video signal or 720p-progressive video signal may be provided from a digital television STB rather than the 480p-progressive video signal.
However, it is assumed that the closed-caption signal Scc is superimposed on the 21H of the 480i video signal. Therefore, if a signal of another mode such as the above-mentioned progressive signal is directly provided to the display apparatus PA as the component video signal Scv, the CC decoder 3 may erroneously detect the provided component video signal Scv and provide an erroneous character display.